This invention relates to a seal unit for mechanical members rotating relative to each other, in particular to foundry rollers.
As is well known, the construction of seal units for members which rotate relative to each other working under particular environmental conditions can give rise to difficulties.
In foundries, for example, solidified material from continuous casting can be transported by means of a plurality of rollers arranged in succession and connected to corresponding shafts through bearings. At their respective ends the rollers are provided with seal units which limit losses of lubricants through the bearings.
Mainly because of the high operating temperatures, special construction arrangements have to be provided for. In more detail, these seal units normally comprise a bush fitted to the corresponding shaft and a plurality of radial metal partitions forming labyrinths between the seat of the bearing and the exterior. Given that labyrinths offer a high level of hydraulic resistance, when the rollers are set in motion the lubricant is retained within the seat of the bearing.
Known sealing units however have some disadvantages, mainly due to the fact that the labyrinths nevertheless permit continuous although limited leakage of lubricant. For this reason it is in fact necessary to provide a pumping unit which makes up for the lubricant which escapes.
Furthermore, lubricant consumption is enormous in that losses cannot be recovered and replaced between the moving parts. In fact, in the course of transport on the rollers, the cast material is cooled with a spray of water and the lubricant which escapes therefore mixes with the cooling water, becoming unusable. Also the disposal of large quantities of lubricant represents a serious disadvantage, from the economic point of view, and also because of the fact that it has an appreciable environmental impact.
A further disadvantage arises from the fact that slag and impurities can enter into the labyrinth passages while in operation, reaching the moving parts and damaging them.
The purpose of this invention is to provide a seal unit which does not have the disadvantages described and which in particular prevents the escape of lubricant under normal conditions of use.
In accordance with this invention a seal unit is constructed for mechanical members which rotate with respect to each other, in particular foundry rollers, comprising a tubular member which can be fitted to a first of said rotating members, characterised in that it comprises a first and a second annular sealing member surrounding said tubular member and provided with a first and second mounting support respectively and corresponding sealing rings of elastomer material, and in that it comprises an annular spacing member coaxial with said tubular member and acts together with said first and second supports to hold said first and second annular sealing members in their respective working positions.
The use of sealing rings of elastomer material makes it possible to achieve an optimum seal and avoid losses of lubricant, which do not therefore have to be made up. As a consequence an appreciable reduction is achieved in the consumption of lubricant and, in addition to this, the need for continuous lubrication of the moving members is overcome. It is therefore possible to achieve appreciable advantages in economic terms and in terms of environmental impact, given that the quantity of lubricant mixed with water which has to be disposed of is considerably reduced. The use of seal units according to the invention is therefore particularly advantageous in that it makes it possible to eliminate the lubricant pumping unit.
Furthermore, the elastomer sealing rings protect the moving members from the accidental ingress of slag, reducing the risk of damage. In a preferred embodiment the seal unit comprises a screen fitted to said first rotating member and placed in contact with said second annular sealing member on the side opposite said first annular sealing member. This makes it possible to further reduce the risk that slag or impurities will reach the moving members.
A further advantage is provided by the fact that the seal unit can easily be mounted in its own working seat. In fact the first and the second annular sealing members assembled with the annular spacer member constitute a seal unit which in turn forms a single assembly with the tubular body. The seal unit can therefore be preassembled and subsequently inserted into its seat in a single operation.